Prior to this invention, copier construction and arrangement is known to have provided sheet bypass capability to feed single sheets or to feed from a bypass stack, either manual or automatic, and to effect duplex copying using such bypass.
U.S. Pat. Nos. 3,645,615; 4,050,805 and 4,098,551 are exemplary of copiers capable of making simplex or duplex copies. When operating in the duplex mode, all necessary side-one copies are automatically diverted to a tray where they then reside in a stack. Subsequently, they are automatically fed out, in a bypass sense, and on a last-in first-out basis, for second-side copying.
U.S. Pat. Nos. 4,110,025 and 4,110,030 show arrangements as above where a single sheet bearing a side-one copy is immediately used, in a bypass sense, for side-two copying, as distinguished from stacking all side-one copies prior to beginning side-two copying.
U.S. Pat. Nos. 3,905,697 and 3,972,612 are exemplary of arrangements where duplex copying is accomplished by manually taking a stack of side-one copies from the copier's exit tray, and inserting them in the copier's original paper supply bin for side-two copying. In U.S. Pat. No. 3,989,236 this function is accomplished by a movable exit tray which swings into the position of the original paper supply tray, and in so doing carries a stack of side-one copies for use as the original paper supply while copying side-two on the blank side thereof.
U.S. Pat. No. 4,017,181 shows arrangements whereby manual sheet bypass is accomplished by providing an original paper feed cassette whose upper horizontal wall includes a slot such that a bypass stack of sheets may be inserted so that the leading edge of this bypass stack replaces the original stack in cooperation with paper feed means. In U.S. Pat. No. 4,087,178 a similar cassette is provided for single sheet bypass. The upper wall of this cassette includes indicia and a registration edge to insure proper manual placement of the bypass sheet.